4. Error Handling

Most Int 31h calls can fail. The DPMI 0.9 specification
does not specify error return codes for most calls. When a
call fails it will set the carry flag and return with the
value in AX unmodified unless otherwise specified. However,
future DPMI implementations will return error codes in the
AX register. All specific error codes will have the high
bit (bit 15) set. If a function returns with carry set and
the high bit of AX clear, it should be treated as a general
failure. Specific error codes will allow programs running
under future DPMI implementations to take appropriate
corrective action in some cases.